Why are expected and observed bands written in a restriction digest report?

Correct answer: For result interpretation and verification

The direct answer is option A: expected and observed bands are recorded so the result can be interpreted and verified. Before running a digest, the DNA sequence, restriction sites, and fragment sizes allow us to predict the expected bands. After electrophoresis, the visible gel gives the observed bands and their approximate sizes. Comparing the two tells us whether digestion probably worked and whether the DNA construct or sample matches the plan. Option A is correct because this comparison supports both interpretation and verification. Option B is wrong: enzyme smell has no role in identifying DNA fragments. Option C is wrong and unsafe as a laboratory idea; agar is a gel material, not something to taste. Option D is wrong because water volume belongs in the reaction setup record, but it is not the reason for writing expected and observed bands. A difference between prediction and observation may arise from incomplete digestion, wrong enzyme, an incorrect sequence assumption, overloaded DNA, or poor size estimation. Memory cue: expected is the prediction; observed is what the gel actually shows.